// Package neovim installs Neovim via pacman, clones the NvChad starter,
// backs up any non-NvChad config, strips the starter's nvim-lspconfig
// block, and writes Archduino's Lua asset files.
package neovim

import (
	"bytes"
	"context"
	"embed"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"text/template"
	"time"

	"github.com/MDietermann/ArduinoArchSetup/internal/config"
	"github.com/MDietermann/ArduinoArchSetup/internal/module"
	"github.com/MDietermann/ArduinoArchSetup/internal/platform"
	"github.com/MDietermann/ArduinoArchSetup/internal/theming"
)

//go:embed assets/*
var assets embed.FS

// Register WriteChadrc with the theming package so theming.Apply can
// rewrite chadrc.lua on theme changes without importing this package
// (which would be a cycle: neovim imports theming).
func init() {
	theming.ChadrcWriter = WriteChadrc
}

// assetMap lists each asset and its destination under ~/.config/nvim.
// Order matters: Detect iterates in this order and Apply writes in this order.
var assetMap = []struct {
	SrcPath string // under assets/
	DstRel  string // under ~/.config/nvim/
}{
	{"assets/arduino.lua", "lua/plugins/arduino.lua"},
	{"assets/dap.lua", "lua/plugins/dap.lua"},
	{"assets/lspconfig.lua", "lua/plugins/lspconfig.lua"},
	{"assets/mappings.lua", "lua/mappings.lua"},
	{"assets/clangd.lua", "lsp/clangd.lua"},
}

// Module installs and configures Neovim + NvChad for Archduino.
type Module struct {
	cfg     config.NeovimConfig
	themeID string
	pm      platform.PackageManager
	git     platform.GitClient
}

// New constructs a Neovim Module.
func New(cfg config.NeovimConfig, themeID string, pm platform.PackageManager, git platform.GitClient) Module {
	return Module{cfg: cfg, themeID: themeID, pm: pm, git: git}
}

type state struct {
	NvimInstalled   bool
	ConfigDirExists bool
	ChadrcPresent   bool
	BackupNeeded    bool
	BackupSource    string
	StarterCloned   bool
	MissingAssets   []string
	ChadrcDrift     bool
	LspconfigBlock  bool
	StarterLspFile  bool
	ThemeName       string
	RenderedChadrc  []byte
}

// Meta returns the module metadata.
func (Module) Meta() module.Meta {
	return module.Meta{ID: "neovim", Name: "Neovim + NvChad", Description: "Install Neovim and configure NvChad with Archduino plugins."}
}

func nvimCfg() (string, error) {
	h, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(h, ".config", "nvim"), nil
}

func (m Module) resolvedTheme() string {
	if t, ok := theming.Get(m.themeID); ok && t.NvChadTheme != "" {
		return t.NvChadTheme
	}
	if list := theming.List(); len(list) > 0 && list[0].NvChadTheme != "" {
		return list[0].NvChadTheme
	}
	return "gruvbox"
}

// WriteChadrc renders chadrc.lua for the given NvChad theme name and writes
// it to ~/.config/nvim/lua/chadrc.lua. If the file does not already exist
// and the surrounding nvim config dir does not exist, the function returns
// nil without writing anything (the user hasn't installed neovim yet).
//
// Exported so the theming package can re-render chadrc on theme switches
// without re-running the full Module pipeline.
func WriteChadrc(nvChadThemeName string) error {
	home, err := os.UserHomeDir()
	if err != nil {
		return err
	}
	cfg := filepath.Join(home, ".config", "nvim")
	chadrcPath := filepath.Join(cfg, "lua", "chadrc.lua")

	// If chadrc doesn't exist, only write when the parent dir exists. A
	// fresh system where nvim was never installed should be a no-op.
	if _, err := os.Stat(chadrcPath); err != nil {
		if _, err := os.Stat(cfg); err != nil {
			return nil
		}
	}

	tmplBytes, err := assets.ReadFile("assets/chadrc.lua.tmpl")
	if err != nil {
		return err
	}
	tmpl, err := template.New("chadrc").Parse(string(tmplBytes))
	if err != nil {
		return err
	}
	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, struct{ NvChadTheme string }{NvChadTheme: nvChadThemeName}); err != nil {
		return err
	}
	return platform.WriteUserFile(chadrcPath, buf.Bytes(), 0o644)
}

func (m Module) renderChadrc() ([]byte, error) {
	tmplBytes, err := assets.ReadFile("assets/chadrc.lua.tmpl")
	if err != nil {
		return nil, err
	}
	tmpl, err := template.New("chadrc").Parse(string(tmplBytes))
	if err != nil {
		return nil, err
	}
	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, struct{ NvChadTheme string }{NvChadTheme: m.resolvedTheme()}); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

// Detect inspects the filesystem and returns the current state.
func (m Module) Detect(ctx context.Context) (module.State, error) {
	cfg, err := nvimCfg()
	if err != nil {
		return nil, err
	}
	var s state
	s.ThemeName = m.resolvedTheme()
	if m.pm != nil {
		ok, err := m.pm.IsInstalled(ctx, "neovim")
		if err != nil {
			return nil, err
		}
		s.NvimInstalled = ok
	}

	rendered, err := m.renderChadrc()
	if err != nil {
		return nil, err
	}
	s.RenderedChadrc = rendered

	if fi, err := os.Stat(cfg); err == nil && fi.IsDir() {
		s.ConfigDirExists = true
		if _, err := os.Stat(filepath.Join(cfg, "lua", "chadrc.lua")); err == nil {
			s.ChadrcPresent = true
		}
		if _, err := os.Stat(filepath.Join(cfg, "lua")); err == nil && !s.ChadrcPresent {
			s.BackupNeeded = true
			s.BackupSource = cfg
		}
	}
	if _, err := os.Stat(filepath.Join(cfg, "lua", "plugins", "init.lua")); err == nil {
		s.StarterCloned = true
		data, _ := os.ReadFile(filepath.Join(cfg, "lua", "plugins", "init.lua"))
		if bytes.Contains(data, []byte("nvim-lspconfig")) {
			s.LspconfigBlock = true
		}
	}
	if _, err := os.Stat(filepath.Join(cfg, "lua", "configs", "lspconfig.lua")); err == nil {
		s.StarterLspFile = true
	}

	if cur, err := os.ReadFile(filepath.Join(cfg, "lua", "chadrc.lua")); err == nil {
		if !bytes.Equal(cur, rendered) {
			s.ChadrcDrift = true
		}
	}

	for _, a := range assetMap {
		want, _ := assets.ReadFile(a.SrcPath)
		got, err := os.ReadFile(filepath.Join(cfg, a.DstRel))
		if err != nil || !bytes.Equal(got, want) {
			s.MissingAssets = append(s.MissingAssets, a.DstRel)
		}
	}
	return s, nil
}

// stripLspconfigBlock removes the plugin-table entry that references
// "neovim/nvim-lspconfig" from the NvChad starter's init.lua. It walks the
// source line-by-line: find the marker line, scan backward for the opening
// `{` of that entry, then scan forward counting braces until the matching
// `}` (plus trailing `,` if present). Robust against nested tables inside
// the entry (e.g. `opts = {}`) that defeat single-level regexes.
func stripLspconfigBlock(src []byte) []byte {
	lines := strings.Split(string(src), "\n")
	markerIdx := -1
	for i, l := range lines {
		if strings.Contains(l, "neovim/nvim-lspconfig") {
			markerIdx = i
			break
		}
	}
	if markerIdx == -1 {
		return src
	}

	// Scan backward for the opening `{` that begins the plugin entry.
	// We track braces relative to the marker line so nested tables on
	// earlier lines don't confuse the search: we want the first `{`
	// whose pair would enclose the marker.
	startLine := -1
	depth := 0
	for i := markerIdx; i >= 0; i-- {
		// Count braces on this line from right to left.
		for j := len(lines[i]) - 1; j >= 0; j-- {
			c := lines[i][j]
			if c == '}' {
				depth++
			} else if c == '{' {
				if depth == 0 {
					startLine = i
					// break out of both loops
					i = -1
					break
				}
				depth--
			}
		}
	}
	if startLine == -1 {
		return src
	}

	// Scan forward from markerIdx for the matching `}`.
	endLine := -1
	depth = 1 // we're already inside the `{` at startLine
	// Start just after the opening `{` on startLine.
	for i := startLine; i < len(lines); i++ {
		start := 0
		if i == startLine {
			// skip past the first `{` on this line
			idx := strings.Index(lines[i], "{")
			if idx >= 0 {
				start = idx + 1
			}
		}
		for j := start; j < len(lines[i]); j++ {
			c := lines[i][j]
			if c == '{' {
				depth++
			} else if c == '}' {
				depth--
				if depth == 0 {
					endLine = i
					break
				}
			}
		}
		if endLine != -1 {
			break
		}
	}
	if endLine == -1 {
		return src
	}

	// Include an optional trailing comma and whitespace-only lines after endLine.
	cutEnd := endLine
	// If the `}` line also has a trailing `,`, that's fine; keep the line as-is
	// but drop it. If the endLine text after the closing `}` is just `,` or
	// `,` + whitespace, keep cutEnd = endLine. Otherwise also keep cutEnd.
	// Skip a single blank line after the block to avoid leaving a stray gap.
	if cutEnd+1 < len(lines) && strings.TrimSpace(lines[cutEnd+1]) == "" {
		cutEnd++
	}

	out := make([]string, 0, len(lines)-(cutEnd-startLine+1))
	out = append(out, lines[:startLine]...)
	out = append(out, lines[cutEnd+1:]...)
	return []byte(strings.Join(out, "\n"))
}

// Plan computes the idempotent set of actions to converge to desired state.
func (m Module) Plan(ctx context.Context, cur module.State) (module.Plan, error) {
	s, _ := cur.(state)
	cfg, err := nvimCfg()
	if err != nil {
		return module.Plan{}, err
	}
	var actions []module.Action

	if !s.NvimInstalled && m.pm != nil {
		actions = append(actions, module.Action{
			Description: "pacman install neovim",
			Kind:        module.ActionPackageInstall,
			Exec:        func(ctx context.Context) error { return m.pm.Install(ctx, []string{"neovim"}) },
		})
	}

	if s.BackupNeeded {
		src := s.BackupSource
		actions = append(actions, module.Action{
			Description: "back up existing non-NvChad config",
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				ts := time.Now().UTC().Format("20060102T150405Z")
				return os.Rename(src, src+".bak."+ts)
			},
		})
	}

	if !s.StarterCloned || s.BackupNeeded {
		repo := m.cfg.NvChadStarterRepo
		actions = append(actions, module.Action{
			Description: "clone NvChad starter",
			Kind:        module.ActionGitClone,
			Exec: func(ctx context.Context) error {
				if err := os.MkdirAll(filepath.Dir(cfg), 0o755); err != nil {
					return err
				}
				if err := m.git.Clone(ctx, repo, cfg); err != nil {
					return err
				}
				return os.RemoveAll(filepath.Join(cfg, ".git"))
			},
		})
	}

	if s.LspconfigBlock || !s.StarterCloned || s.BackupNeeded {
		actions = append(actions, module.Action{
			Description: "strip nvim-lspconfig block from starter init.lua",
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				p := filepath.Join(cfg, "lua", "plugins", "init.lua")
				data, err := os.ReadFile(p)
				if err != nil {
					return err
				}
				return platform.WriteUserFile(p, stripLspconfigBlock(data), 0o644)
			},
		})
	}

	if s.StarterLspFile || !s.StarterCloned || s.BackupNeeded {
		actions = append(actions, module.Action{
			Description: "remove starter lspconfig.lua",
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				err := os.Remove(filepath.Join(cfg, "lua", "configs", "lspconfig.lua"))
				if err != nil && !os.IsNotExist(err) {
					return err
				}
				return nil
			},
		})
	}

	if s.ChadrcDrift || !s.ChadrcPresent || s.BackupNeeded {
		rendered := append([]byte{}, s.RenderedChadrc...)
		actions = append(actions, module.Action{
			Description: "write chadrc.lua with theme " + s.ThemeName,
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				return platform.WriteUserFile(filepath.Join(cfg, "lua", "chadrc.lua"), rendered, 0o644)
			},
		})
	}

	for _, dst := range s.MissingAssets {
		dst := dst
		actions = append(actions, module.Action{
			Description: "write asset " + dst,
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				var src string
				for _, a := range assetMap {
					if a.DstRel == dst {
						src = a.SrcPath
						break
					}
				}
				data, err := assets.ReadFile(src)
				if err != nil {
					return err
				}
				return platform.WriteUserFile(filepath.Join(cfg, dst), data, 0o644)
			},
		})
	}

	if len(actions) > 0 {
		actions = append(actions, module.Action{
			Description: "clear NvChad base46 theme cache",
			Kind:        module.ActionFileWrite,
			Exec: func(ctx context.Context) error {
				home, _ := os.UserHomeDir()
				_ = os.RemoveAll(filepath.Join(home, ".local", "share", "nvim", "lazy", "base46", "lua", "base46", "themes"))
				_ = os.RemoveAll(filepath.Join(home, ".cache", "nvim", "base46"))
				return nil
			},
		})
	}

	return module.Plan{Actions: actions}, nil
}

// Apply executes the planned actions in order.
func (m Module) Apply(ctx context.Context, p module.Plan, r module.Reporter) error {
	for i, a := range p.Actions {
		r.Progress(m.Meta().ID, i+1, len(p.Actions), a.Description)
		if err := a.Exec(ctx); err != nil {
			return err
		}
	}
	return nil
}

// Verify re-Detects and returns an error if state is not converged.
func (m Module) Verify(ctx context.Context) error {
	st, err := m.Detect(ctx)
	if err != nil {
		return err
	}
	s := st.(state)
	if !s.NvimInstalled {
		return fmt.Errorf("neovim not installed")
	}
	if !s.ChadrcPresent {
		return fmt.Errorf("chadrc.lua missing")
	}
	if s.ChadrcDrift {
		return fmt.Errorf("chadrc.lua content drifted")
	}
	if len(s.MissingAssets) > 0 {
		return fmt.Errorf("missing assets: %v", s.MissingAssets)
	}
	if s.LspconfigBlock {
		return fmt.Errorf("nvim-lspconfig block not stripped")
	}
	if s.StarterLspFile {
		return fmt.Errorf("starter lspconfig.lua still present")
	}
	return nil
}