package chatd

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"net/http"
	"path"
	"regexp"
	"strings"

	"golang.org/x/xerrors"

	"github.com/coder/coder/v2/coderd/database"
	"github.com/coder/coder/v2/coderd/x/chatd/chattool"
	"github.com/coder/coder/v2/codersdk"
	"github.com/coder/coder/v2/codersdk/workspacesdk"
)

const (
	maxInstructionFileBytes = 64 * 1024
)

var markdownCommentPattern = regexp.MustCompile(`<!--[\s\S]*?-->`)

// readHomeInstructionFile reads an instruction file from the
// agent's home directory using home-relative path resolution.
// This is the fallback for older agents that don't support
// the context-config endpoint.
func readHomeInstructionFile(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	homeDir string,
	fileName string,
) (content string, sourcePath string, truncated bool, err error) {
	if conn == nil {
		return "", "", false, nil
	}

	dirListing, err := conn.LS(ctx, "", workspacesdk.LSRequest{
		Path:       []string{homeDir},
		Relativity: workspacesdk.LSRelativityHome,
	})
	if err != nil {
		if isCodersdkStatusCode(err, http.StatusNotFound) {
			return "", "", false, nil
		}
		return "", "", false, xerrors.Errorf("list home instruction directory: %w", err)
	}

	var filePath string
	for _, entry := range dirListing.Contents {
		if entry.IsDir {
			continue
		}
		if strings.EqualFold(strings.TrimSpace(entry.Name), fileName) {
			filePath = strings.TrimSpace(entry.AbsolutePathString)
			break
		}
	}
	if filePath == "" {
		return "", "", false, nil
	}

	return readInstructionFile(ctx, conn, filePath)
}

// readInstructionDirFile reads an instruction file from the given
// absolute directory path. The directory is listed and scanned
// for a file matching fileName (case-insensitive).
func readInstructionDirFile(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	absDir string,
	fileName string,
) (content string, sourcePath string, truncated bool, err error) {
	if conn == nil {
		return "", "", false, nil
	}

	dirListing, err := conn.LS(ctx, "", workspacesdk.LSRequest{
		Path:       []string{absDir},
		Relativity: workspacesdk.LSRelativityRoot,
	})
	if err != nil {
		if isCodersdkStatusCode(err, http.StatusNotFound) {
			return "", "", false, nil
		}
		return "", "", false, xerrors.Errorf("list instruction directory: %w", err)
	}

	var filePath string
	for _, entry := range dirListing.Contents {
		if entry.IsDir {
			continue
		}
		if strings.EqualFold(strings.TrimSpace(entry.Name), fileName) {
			filePath = strings.TrimSpace(entry.AbsolutePathString)
			break
		}
	}
	if filePath == "" {
		return "", "", false, nil
	}

	return readInstructionFile(ctx, conn, filePath)
}

// readInstructionFile reads and sanitizes an instruction file at the
// given absolute path.
func readInstructionFile(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	filePath string,
) (content string, sourcePath string, truncated bool, err error) {
	reader, _, err := conn.ReadFile(
		ctx,
		filePath,
		0,
		maxInstructionFileBytes+1,
	)
	if err != nil {
		if isCodersdkStatusCode(err, http.StatusNotFound) {
			return "", "", false, nil
		}
		return "", "", false, xerrors.Errorf("read instruction file: %w", err)
	}
	defer reader.Close()

	raw, err := io.ReadAll(reader)
	if err != nil {
		return "", "", false, xerrors.Errorf("read instruction bytes: %w", err)
	}

	truncated = int64(len(raw)) > maxInstructionFileBytes
	if truncated {
		raw = raw[:maxInstructionFileBytes]
	}

	content = sanitizeInstructionMarkdown(string(raw))
	if content == "" {
		return "", "", truncated, nil
	}

	return content, filePath, truncated, nil
}

func sanitizeInstructionMarkdown(content string) string {
	content = markdownCommentPattern.ReplaceAllString(content, "")
	content = SanitizePromptText(content)
	return strings.TrimSpace(content)
}

// formatSystemInstructions builds the <workspace-context> block from
// agent metadata and zero or more instruction file sections.
func formatSystemInstructions(
	operatingSystem, directory string,
	sections []instructionFileSection,
) string {
	hasSections := false
	for _, s := range sections {
		if s.content != "" {
			hasSections = true
			break
		}
	}
	if !hasSections && operatingSystem == "" && directory == "" {
		return ""
	}

	var b strings.Builder
	_, _ = b.WriteString("<workspace-context>\n")
	if operatingSystem != "" {
		_, _ = b.WriteString("Operating System: ")
		_, _ = b.WriteString(operatingSystem)
		_, _ = b.WriteString("\n")
	}
	if directory != "" {
		_, _ = b.WriteString("Working Directory: ")
		_, _ = b.WriteString(directory)
		_, _ = b.WriteString("\n")
	}
	for _, s := range sections {
		if s.content == "" {
			continue
		}
		_, _ = b.WriteString("\nSource: ")
		_, _ = b.WriteString(s.source)
		if s.truncated {
			_, _ = b.WriteString(" (truncated to 64KiB)")
		}
		_, _ = b.WriteString("\n")
		_, _ = b.WriteString(s.content)
		_, _ = b.WriteString("\n")
	}
	_, _ = b.WriteString("</workspace-context>")
	return b.String()
}

// instructionFileSection is a single instruction file's content and
// source path for rendering inside <workspace-context>.
type instructionFileSection struct {
	content   string
	source    string
	truncated bool
}

// instructionFromContextFiles reconstructs the formatted instruction
// string from persisted context-file parts. This is used on non-first
// turns so the instruction can be re-injected after compaction
// without re-dialing the workspace agent.
func instructionFromContextFiles(
	messages []database.ChatMessage,
) string {
	var sections []instructionFileSection
	var os, dir string
	for _, msg := range messages {
		if !msg.Content.Valid ||
			!bytes.Contains(msg.Content.RawMessage, []byte(`"context-file"`)) {
			continue
		}
		var parts []codersdk.ChatMessagePart
		if err := json.Unmarshal(msg.Content.RawMessage, &parts); err != nil {
			continue
		}
		for _, part := range parts {
			if part.Type != codersdk.ChatMessagePartTypeContextFile {
				continue
			}
			if part.ContextFileOS != "" {
				os = part.ContextFileOS
			}
			if part.ContextFileDirectory != "" {
				dir = part.ContextFileDirectory
			}
			if part.ContextFileContent != "" {
				sections = append(sections, instructionFileSection{
					content:   part.ContextFileContent,
					source:    part.ContextFilePath,
					truncated: part.ContextFileTruncated,
				})
			}
		}
	}
	return formatSystemInstructions(os, dir, sections)
}

// skillsFromParts reconstructs skill metadata from persisted
// skill parts. This is analogous to instructionFromContextFiles
// so the skill index can be re-injected after compaction without
// re-dialing the workspace agent.
func skillsFromParts(
	messages []database.ChatMessage,
) []chattool.SkillMeta {
	var skills []chattool.SkillMeta
	for _, msg := range messages {
		if !msg.Content.Valid ||
			!bytes.Contains(msg.Content.RawMessage, []byte(`"skill"`)) {
			continue
		}
		var parts []codersdk.ChatMessagePart
		if err := json.Unmarshal(msg.Content.RawMessage, &parts); err != nil {
			continue
		}
		for _, part := range parts {
			if part.Type != codersdk.ChatMessagePartTypeSkill {
				continue
			}
			skills = append(skills, chattool.SkillMeta{
				Name:        part.SkillName,
				Description: part.SkillDescription,
				Dir:         part.SkillDir,
			})
		}
	}
	return skills
}

// pwdInstructionFilePath returns the absolute path to the
// instruction file in the given working directory, or empty if
// directory is empty.
func pwdInstructionFilePath(directory, fileName string) string {
	if directory == "" || fileName == "" {
		return ""
	}
	return path.Join(directory, fileName)
}

// skillMetaFileFromParts scans persisted context-file parts for
// the stored skill meta file name. Uses last-wins semantics to
// match contextFileAgentID, so after an agent change the newest
// agent's value is returned.
func skillMetaFileFromParts(
	messages []database.ChatMessage,
) string {
	var result string
	for _, msg := range messages {
		if !msg.Content.Valid ||
			!bytes.Contains(msg.Content.RawMessage, []byte(`"context-file"`)) {
			continue
		}
		var parts []codersdk.ChatMessagePart
		if err := json.Unmarshal(msg.Content.RawMessage, &parts); err != nil {
			continue
		}
		for _, part := range parts {
			if part.Type != codersdk.ChatMessagePartTypeContextFile {
				continue
			}
			if part.ContextFileSkillMetaFile != "" {
				result = part.ContextFileSkillMetaFile
			}
		}
	}
	return result
}

func isCodersdkStatusCode(err error, statusCode int) bool {
	var sdkErr *codersdk.Error
	if !xerrors.As(err, &sdkErr) {
		return false
	}
	return sdkErr.StatusCode() == statusCode
}