package handler

import (
	"errors"
	"fmt"
	"net/http"
	"strings"

	"github.com/agentmail/gateway/internal/middleware"
	"github.com/agentmail/gateway/internal/models"
	"github.com/agentmail/gateway/internal/repo"
	"github.com/go-chi/chi/v5"
	"github.com/google/uuid"
)

// ---------- 转发 ----------
//
// 转发 = 引用原文 + 新收件人。与「回复」的区别：
//   回复（reply_to）落回原会话，收件人是原发件人；
//   转发按目标地址的 session 位另行定位会话，收件人是新指定的人。
// 因此转发不复用 reply_to，而是走完整的三维寻址。

type forwardRequest struct {
	// To 新收件人，完整三维地址
	To string `json:"to"`
	// CC 可选抄送
	CC string `json:"cc"`
	// Comment 转发者附加的说明，置于引用原文之前
	Comment string `json:"comment"`
	// Subject 可选；留空时自动加 "Fwd: " 前缀
	Subject string `json:"subject"`
	// SessionAlias 仅在目标地址以 .new 结尾时生效
	SessionAlias string `json:"session_alias"`
}

// quoteBody 把原文渲染为 Markdown 引用块。
// 逐行加 "> " 而不是整段包裹：原文本身可能含代码块与列表，
// 只有逐行前缀才能在任何 Markdown 渲染器里保持引用语义。
func quoteBody(m *models.Mail) string {
	var b strings.Builder
	b.WriteString("---\n\n")
	b.WriteString(fmt.Sprintf("> **转发自** %s", m.FromName))
	if m.FromWorkspace != "" {
		b.WriteString("@" + m.FromWorkspace)
	}
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf("> **主题** %s\n", m.Subject))
	b.WriteString(fmt.Sprintf("> **时间** %s\n", m.CreatedAt.Format("2006-01-02 15:04:05")))
	if len(m.CCList) > 0 {
		names := make([]string, 0, len(m.CCList))
		for _, c := range m.CCList {
			names = append(names, c.Raw)
		}
		b.WriteString(fmt.Sprintf("> **抄送** %s\n", strings.Join(names, ", ")))
	}
	b.WriteString(">\n")
	for _, line := range strings.Split(m.Body, "\n") {
		b.WriteString("> " + line + "\n")
	}
	return b.String()
}

// forwardSubject 生成转发主题，避免 "Fwd: Fwd: Fwd:" 无限叠加。
func forwardSubject(custom, original string) string {
	if s := strings.TrimSpace(custom); s != "" {
		return s
	}
	if strings.HasPrefix(original, "Fwd: ") {
		return original
	}
	return "Fwd: " + original
}

// doForward 是 Agent 与人类两条转发路径的公共实现。
// actor 是转发者名（Agent 名或用户名），fromWorkspace 仅 Agent 有。
func doForward(w http.ResponseWriter, r *http.Request, mailID uuid.UUID, actor, fromWorkspace string, isAgent bool) {
	var req forwardRequest
	if err := Decode(r, &req); err != nil {
		Error(w, http.StatusBadRequest, "Invalid JSON")
		return
	}
	if strings.TrimSpace(req.To) == "" {
		Error(w, http.StatusBadRequest, "Missing to")
		return
	}

	src, err := repo.LoadForwardSource(r.Context(), mailID, actor)
	switch {
	case errors.Is(err, repo.ErrMailNotFound):
		Error(w, http.StatusNotFound, "待转发的邮件不存在")
		return
	case errors.Is(err, repo.ErrForwardNotAllowed):
		Error(w, http.StatusForbidden, "只能转发自己参与过的邮件")
		return
	case err != nil:
		Error(w, http.StatusInternalServerError, "Failed to load mail")
		return
	}

	to, err := models.ParseAddress(req.To)
	if err != nil {
		Error(w, http.StatusBadRequest, "Invalid to address: "+err.Error())
		return
	}
	ccList, err := models.ParseAddressList(req.CC)
	if err != nil {
		Error(w, http.StatusBadRequest, "Invalid cc address: "+err.Error())
		return
	}

	user := middleware.GetUser(r)
	if !isAgent && user != nil {
		to = resolveHumanAlias(to, user.Username)
		for i := range ccList {
			ccList[i] = resolveHumanAlias(ccList[i], user.Username)
		}
		if msg := checkScope(r, user, append([]models.Address{to}, ccList...)); msg != "" {
			Error(w, http.StatusForbidden, msg)
			return
		}
	}

	subject := forwardSubject(req.Subject, src.Subject)

	// 转发按目标地址寻址，不带 reply_to：它是一条新线索，不该并进原会话
	sessionID, _, err := resolveTarget(r, to, "", actor, subject, req.SessionAlias)
	if err != nil {
		writeErr(w, err, "Failed to resolve session")
		return
	}

	if isAgent {
		quota, qErr := repo.ConsumeQuota(r.Context(), actor)
		if errors.Is(qErr, repo.ErrQuotaExhausted) {
			Error(w, http.StatusForbidden, fmt.Sprintf(
				"发信配额已用尽（%d/%d）。请先向人类发送最终总结，或联系管理员重置配额。",
				quota.Used, quota.Max))
			return
		}
		if qErr != nil {
			Error(w, http.StatusInternalServerError, "Failed to check quota")
			return
		}
	} else if user != nil {
		_ = repo.SetSessionOwner(r.Context(), sessionID, user.ID)
	}

	body := quoteBody(src)
	if c := strings.TrimSpace(req.Comment); c != "" {
		body = c + "\n\n" + body
	}
	attachedCount := 0

	// parent_mail_id 指向原邮件：即便落在新会话里，也能回溯这封转发从何而来
	newID, err := repo.CreateMail(r.Context(), sessionID, &src.ID,
		actor, fromWorkspace, to.Name, to.Path, subject, body, ccList)
	if err != nil {
		Error(w, http.StatusInternalServerError, "Failed to create mail")
		return
	}

	// 附件随转发一同带过去——只引用正文而丢掉附件，收件人拿到的是一封残缺的邮件。
	// 内容寻址下这只是新增元数据，不拷磁盘文件。
	if n, err := repo.CopyAttachmentsTo(r.Context(), src.ID, newID, actor); err != nil {
		Error(w, http.StatusInternalServerError, "复制附件失败")
		return
	} else {
		attachedCount = n
	}

	notifyRecipients(to, ccList, sessionID, newID, actor, subject)

	JSON(w, http.StatusOK, map[string]any{
		"mail_id":        newID.String(),
		"session_id":     sessionID.String(),
		"session_alias":  repo.SessionAliasOf(r.Context(), sessionID),
		"forwarded_from": src.ID.String(),
		"attachments":    attachedCount,
	})
}

// POST /api/v1/mail/{id}/forward —— Agent 侧转发
func ForwardMail(w http.ResponseWriter, r *http.Request) {
	agentName := middleware.GetAgentName(r)
	if agentName == "" {
		Error(w, http.StatusUnauthorized, "Unauthorized")
		return
	}
	mailID, ok := pathUUID(w, r, "id")
	if !ok {
		return
	}
	doForward(w, r, mailID, agentName, agentName, true)
}

// POST /api/v1/me/mail/{id}/forward —— 人类侧转发
func MeForwardMail(w http.ResponseWriter, r *http.Request) {
	user := middleware.GetUser(r)
	if user == nil {
		Error(w, http.StatusUnauthorized, "not authenticated")
		return
	}
	mailID, ok := pathUUID(w, r, "id")
	if !ok {
		return
	}
	doForward(w, r, mailID, user.Username, "", false)
}

// ---------- 配额管理（管理员） ----------

// GET /api/v1/admin/quotas
func AdminListQuotas(w http.ResponseWriter, r *http.Request) {
	quotas, err := repo.ListQuotas(r.Context())
	if err != nil {
		Error(w, http.StatusInternalServerError, "Failed to list quotas")
		return
	}
	JSON(w, http.StatusOK, map[string]any{"quotas": quotas})
}

type setQuotaRequest struct {
	// MaxRounds 发信配额上限；0 = 不限
	MaxRounds *int `json:"max_rounds"`
	// Reset 为 true 时把已用次数归零
	Reset bool `json:"reset"`
}

// PUT /api/v1/admin/quotas/{name}
func AdminSetQuota(w http.ResponseWriter, r *http.Request) {
	name := strings.TrimSpace(chi.URLParam(r, "name"))
	if name == "" {
		Error(w, http.StatusBadRequest, "Missing agent name")
		return
	}

	var req setQuotaRequest
	if err := Decode(r, &req); err != nil {
		Error(w, http.StatusBadRequest, "Invalid JSON")
		return
	}
	if req.MaxRounds == nil && !req.Reset {
		Error(w, http.StatusBadRequest, "需要 max_rounds 或 reset 之一")
		return
	}

	var (
		q   repo.Quota
		err error
	)
	if req.MaxRounds != nil {
		if q, err = repo.SetQuota(r.Context(), name, *req.MaxRounds); err != nil {
			Error(w, http.StatusNotFound, err.Error())
			return
		}
	}
	if req.Reset {
		if q, err = repo.ResetQuota(r.Context(), name); err != nil {
			Error(w, http.StatusNotFound, err.Error())
			return
		}
	}
	JSON(w, http.StatusOK, map[string]any{"quota": q})
}