package api

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"os/exec"
	"strings"
	"time"
)

const elaborateTimeout = 30 * time.Second

// claudeJSONResult is the top-level object returned by `claude --output-format json`.
type claudeJSONResult struct {
	Result  string `json:"result"`
	IsError bool   `json:"is_error"`
}

// geminiJSONResult is the top-level object returned by `gemini --output-format json`.
type geminiJSONResult struct {
	Response string `json:"response"`
}

// extractJSON returns the first top-level JSON object found in s, stripping
// surrounding prose or markdown code fences the model may have added.
func extractJSON(s string) string {
	start := strings.Index(s, "{")
	end := strings.LastIndex(s, "}")
	if start == -1 || end == -1 || end < start {
		return s
	}
	return s[start : end+1]
}

func (s *Server) claudeBinaryPath() string {
	if s.elaborateCmdPath != "" {
		return s.elaborateCmdPath
	}
	if s.claudeBinPath != "" {
		return s.claudeBinPath
	}
	return "claude"
}

func (s *Server) geminiBinaryPath() string {
	if s.geminiBinPath != "" {
		return s.geminiBinPath
	}
	return "gemini"
}

// elaboratedStorySubtask is a leaf unit within a story task.
type elaboratedStorySubtask struct {
	Name         string `json:"name"`
	Instructions string `json:"instructions"`
}

// elaboratedStoryTask is one independently-deployable unit in a story plan.
type elaboratedStoryTask struct {
	Name               string                   `json:"name"`
	Instructions       string                   `json:"instructions"`
	AcceptanceCriteria string                   `json:"acceptance_criteria"`
	Subtasks           []elaboratedStorySubtask `json:"subtasks"`
}

// elaboratedStoryValidation describes how to verify the story was successful.
type elaboratedStoryValidation struct {
	Type            string   `json:"type"`
	Steps           []string `json:"steps"`
	SuccessCriteria string   `json:"success_criteria"`
}

// elaboratedStory is the full implementation plan produced by story elaboration.
type elaboratedStory struct {
	Name       string                    `json:"name"`
	BranchName string                    `json:"branch_name"`
	Tasks      []elaboratedStoryTask     `json:"tasks"`
	Validation elaboratedStoryValidation `json:"validation"`
}

func buildStoryElaboratePrompt() string {
	return `You are a software architect. Given a goal, analyze the codebase at /workspace and produce a structured implementation plan as JSON.

Output ONLY valid JSON matching this schema:
{
  "name": "story name",
  "branch_name": "story/kebab-case-name",
  "tasks": [
    {
      "name": "task name",
      "instructions": "detailed instructions including file paths and what to change",
      "acceptance_criteria": "specific, verifiable conditions a separate reviewer can check — e.g. 'run go test ./... and verify all pass; confirm GET /api/foo returns 200 with expected JSON shape'",
      "subtasks": [
        { "name": "subtask name", "instructions": "..." }
      ]
    }
  ],
  "validation": {
    "type": "build|test|smoke",
    "steps": ["step1", "step2"],
    "success_criteria": "what success looks like"
  }
}

Rules:
- Tasks must be independently buildable (each can be deployed alone)
- Subtasks within a task are order-dependent and run sequentially
- Instructions must include specific file paths, function names, and exact changes
- Instructions must end with: git add -A && git commit -m "..." && git push origin <branch>
- Validation should match the scope: small change = build check; new feature = smoke test
- acceptance_criteria must be concrete and verifiable by a separate agent — no vague assertions like "code looks good"`
}

func (s *Server) elaborateStoryWithClaude(ctx context.Context, workDir, goal string) (*elaboratedStory, error) {
	cmd := exec.CommandContext(ctx, s.claudeBinaryPath(),
		"-p", goal,
		"--system-prompt", buildStoryElaboratePrompt(),
		"--output-format", "json",
		"--model", "haiku",
	)
	if workDir != "" {
		cmd.Dir = workDir
	}

	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	err := cmd.Run()

	output := stdout.Bytes()
	if len(output) == 0 {
		if err != nil {
			return nil, fmt.Errorf("claude failed: %w (stderr: %s)", err, stderr.String())
		}
		return nil, fmt.Errorf("claude returned no output")
	}

	var wrapper claudeJSONResult
	if jerr := json.Unmarshal(output, &wrapper); jerr != nil {
		return nil, fmt.Errorf("failed to parse claude JSON wrapper: %w (output: %s)", jerr, string(output))
	}
	if wrapper.IsError {
		return nil, fmt.Errorf("claude error: %s", wrapper.Result)
	}

	var result elaboratedStory
	if jerr := json.Unmarshal([]byte(extractJSON(wrapper.Result)), &result); jerr != nil {
		return nil, fmt.Errorf("failed to parse elaborated story JSON: %w (result: %s)", jerr, wrapper.Result)
	}
	return &result, nil
}

func (s *Server) elaborateStoryWithGemini(ctx context.Context, workDir, goal string) (*elaboratedStory, error) {
	combinedPrompt := fmt.Sprintf("%s\n\n%s", buildStoryElaboratePrompt(), goal)
	cmd := exec.CommandContext(ctx, s.geminiBinaryPath(),
		"-p", combinedPrompt,
		"--output-format", "json",
		"--model", "gemini-2.5-flash-lite",
	)
	if workDir != "" {
		cmd.Dir = workDir
	}

	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		return nil, fmt.Errorf("gemini failed: %w (stderr: %s)", err, stderr.String())
	}

	var wrapper geminiJSONResult
	if err := json.Unmarshal(stdout.Bytes(), &wrapper); err != nil {
		return nil, fmt.Errorf("failed to parse gemini JSON wrapper: %w (output: %s)", err, stdout.String())
	}

	var result elaboratedStory
	if err := json.Unmarshal([]byte(extractJSON(wrapper.Response)), &result); err != nil {
		return nil, fmt.Errorf("failed to parse elaborated story JSON: %w (response: %s)", err, wrapper.Response)
	}
	return &result, nil
}

func (s *Server) handleElaborateStory(w http.ResponseWriter, r *http.Request) {
	var input struct {
		Goal      string `json:"goal"`
		ProjectID string `json:"project_id"`
	}
	if err := json.NewDecoder(r.Body).Decode(&input); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid JSON: " + err.Error()})
		return
	}
	if input.Goal == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "goal is required"})
		return
	}
	if input.ProjectID == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "project_id is required"})
		return
	}

	proj, err := s.store.GetProject(input.ProjectID)
	if err != nil {
		writeJSON(w, http.StatusNotFound, map[string]string{"error": "project not found"})
		return
	}

	// Update git refs without modifying the working tree.
	if proj.LocalPath != "" {
		gitCmd := exec.Command("git", "-C", proj.LocalPath, "fetch", "origin")
		if err := gitCmd.Run(); err != nil {
			s.logger.Warn("story elaborate: git fetch failed", "error", err, "path", proj.LocalPath)
		}
	}

	ctx, cancel := context.WithTimeout(r.Context(), elaborateTimeout)
	defer cancel()

	result, err := s.elaborateStoryWithClaude(ctx, proj.LocalPath, input.Goal)
	if err != nil {
		s.logger.Warn("story elaborate: claude failed, falling back to gemini", "error", err)
		result, err = s.elaborateStoryWithGemini(ctx, proj.LocalPath, input.Goal)
		if err != nil {
			s.logger.Error("story elaborate: fallback gemini also failed", "error", err)
			writeJSON(w, http.StatusBadGateway, map[string]string{
				"error": fmt.Sprintf("elaboration failed: %v", err),
			})
			return
		}
	}

	if result.Name == "" {
		writeJSON(w, http.StatusBadGateway, map[string]string{
			"error": "elaboration failed: missing required fields in response",
		})
		return
	}

	writeJSON(w, http.StatusOK, result)
}